It is well known to those skilled in the art that the polyhaptate nature of the cyclopentadienyl anion confers unique properties to polymerization catalysts derived therefrom such as stability toward ligand loss or exchange and occupation of several coordination sites on the metal center (e.g. three in the pseudo octahedral environment of CpCr(CO)3) so that its coordination environment is controlled and well defined. This results in more single sited behavior of the catalyst systems relative to e.g. Ziegler-Natta TiCl4/aluminum alkyl based systems, conferring all the benefits of single sited nature such as narrow distributions of molecular weight and comonomer and “tunability” of catalyst performance by variations in the polyhaptate ligand. For the purposes of the description of the invention in this section, “polyhaptate” is taken to mean a ligand that contacts a metal center in a bonding interaction through more than one atom, whether the polyhaptate ligand has a formal charge or is neutral. Thus the “neutral polyhaptate ligand” will contact the transition metal through at least two atoms which are not considered to have a localized, negative charge or a negative charge delocalized between them as in cyclopentadienide. Similarly, the “tethered or bulky monoanionic ligand” may be polyhaptate and will have a negative charge. It is further well known that addition of a second cyclopentadienyl ligand or a tethered anionic ligand to form biscyclopentadienyl complexes or e.g. dimethylsilylbridged cyclopentadienylamide (so called “constrained geometry”) complexes results in improved performance relative to the more open, less sterically locked complexes such as CpZrCl3, CpZr(OR)3, or CpTiCl3 and the like which generally show broader comonomer and molecular weight distributions associated with a multi-sited nature as well as lower activity. Thus the favored “well defined ligand sets” contain a polyhaptate ligand with a bridged monohaptate ligand or an optionally bridged second polyhaptate ligand. Generally in the art the preferred “well defined” catalysts systems use: polyhaptate dianionic ligand sets such as biscyclopentadienyl or bridged cyclopentadienylamido; they use Group 4 metals, especially Zr and Ti; the metals are in their highest oxidation state and are accepted to be cationic with one alkyl or polymer ligand for chain propagation and one open coordination site for olefin coordination prior to or concurrent with insertion; there are no other labile ligands e.g. chloride, alkoxide, carboxylate left on the metal; and a weakly or “non” coordinating anion balances charge. Some nickel-based systems recently reported both by Johnson at DuPont and Grubbs at Caltech are believed effective in the neutral form. In order to maintain the favorable coordination environment of the polyhaptate dianionic ligand sets while using transition metals other than Group 4, many have substituted one or both anionic cyclopentadienyl (Cp) or amido ligands with isoelectronic dianionic analogues. Thus Bazan's substitution of one Cp with a dianionic borrole (C4H4BR2−) allows synthesis of Group 5 complexes in their highest oxidation state while preserving as many of the characteristics of the preferred “well defined ligand set” systems as possible. Similarly Gibson's substitution of two Cps with dianionic imido ligands yields chromium catalysts in their highest oxidation state. This strategy only allows the preparation of cationic catalysts from Groups 5 or higher, while neutral versions could be made for Group 4 or higher. Much less common has been the strategy to maintain one polyhaptate anionic ligand such as Cp and use a tethered neutral ligand to create the “well defined” ligand set. This approach allows the preparation of Group 3 analogues and catalysts from any group in the 3+ oxidation state or lower.
We are not aware of anyone using the approach of substituting the polyhaptate anionic ligand such as Cp with a polyhaptate neutral ligand and an anionic ligand, both selected to provide a “well defined” i.e. relatively non labile ligand set. This has the advantage of allowing a valence to offset the anionic propagating polymer chain and a valence to create a positive charge with an open coordination site if desired. Many polyhaptate ligands offer far more structural diversity and ease of synthesis than e.g. substituted Cps, e.g. hexahydrotriazines made from the condensation of formaldehyde with amines. This could allow the use of any transition metal with a readily accessible 3+ oxidation state such as Sc, Y, La, lanthamides and actinides, V, Nb, Cr, Co, etc. It is this concept that is embodied in the present invention. It is not anticipated that the active species must be cationic or must be in a 3+ oxidation state because those skilled in the art will know that neutral complexes or lower oxidation states may prove competent for catalysts, or that the exact nature of the active species may be difficult to prove when it is derived e.g. from a lower oxidation state starting material. Rather, the catalysts of the invention will be distinguished in that they contain at least a neutral polyhaptate ligand and an anionic ligand, for which said anionic ligand will be either bridged to the polyhaptate ligand or be of a size to afford some degree of steric protection against its substitution.
Neutral scandium compounds having two univalent ligands or a bidentate, divalent ligand are known from Shapiro et al., Organometallics, vol. 9, pp. 867–869 (1990); Piers et al., J. Am. Chem. Soc., vol. 112, pp. 9406–9407 (1990); Shapiro et al., J. Am. Chem. Soc., vol. 116, pp. 4623–4640 (1994); Hajela et al., Organometallics, vol. 13, pp. 1147–1154 (1994); and U.S. Pat. No. 5,563,219 to Yasuda et al. Similar yttrium, lanthanum and cerium complexes are disclosed in Booij et al., Journal of Organometallic Chemistry, vol. 364, pp. 79–86 (1989) and Coughlin et al., J. Am. Chem. Soc., vol. 114, pp. 7606–7607 (1992). Polymerization with a metal scandium complex having a bidentate, divalent ligand using a non-ionizing cocatalyst is known from U.S. Pat. No. 5,464,906 to Patton et al.
Group-3-10 metallocyclic catalyst complexes are described in U.S. Pat. Nos. 5,312,881 and 5,455,317, both to Marks et al.; U.S. Pat. No. 5,064,802 to Stevens et al.; and EP 0 765 888 A2.
Polymerization of olefins with cationic Group-4 metal complexes is illustrated in WO 96/13529 and WO 97/42228. Boratabenzene complexes of Group-3-5 metals are disclosed in WO 97/23493.
Amidinato complexes of Group-3-6 metals are disclosed in U.S. Pat. No. 5,707,913 to Schlund et al. Group 4 bisamido catalysts are disclosed in U.S. Pat. No. 5,318,935 to Canich, et al., and related multidentate bisarylamido catalysts are disclosed by D. H. McConville, et al, Macromolecules 1996, 29, 5241–5243.
Monoanionic and Polyhaptate Ligands for Catalysis.
While replacing Cp− ligands with dianionic formal 6 electron donors has been known to give active catalysts if the metal identity or number of labile ligands are adjusted to maintain an “isoelectronic” state, the practice of using 6 electron neutral donor ligands has received little attention. We believe that the ligand set defined by a neutral polyhaptate donor optionally bridged to a monoanionic donor are suited to stabilize lanthamides, actinides, and group 3 metals, TiIII, VIII, CrIII, FeIII, and CoIII in configurations with two labile ligands such as chloride in such a way as to promote polymerization activity with a suitable activator. It is depicted as follows:(L)T(E)MQxL′y(where T=optional bridge, L=polyhaptate neutral donor ligand, E=monoanionic ligand, M=a metal, preferably in the 3+ oxidation state, Q=labile ligands such as chloride, methyl, etc., L′=neutral donor ligands such as ethers, phosphines, amines, LiCl, olefins, cyclooctadiene). Versions with a single Q ligand for Fell etc. could readily be envisioned.